Non-self-luminous display apparatuses represented by liquid crystal display apparatuses have backlight apparatuses (hereinafter, simply “backlight”) in the back. These display apparatuses display images through an optical modulating section. According to image signals, the optical modulating section adjusts the reflectance or transmittance of light emitted from the backlight. To expand the dynamic range of display brightness, these display apparatuses employ a configuration where the illuminating section of the backlight is divided into a plurality of areas and brightness is controlled on a per area basis.
With the configuration as described above, in terms of cost, it is difficult to make the number of divisions of the backlight (i.e. the resolution of the backlight) the same as the resolution of the optical modulating section. Accordingly, the resolution of the backlight is usually lower than the resolution of the optical modulating section. Therefore, problems occur due to the difference in resolution between the backlight and the optical modulating section. One of the problems is the phenomenon where a part that must be displayed in black becomes bright and appears distinctly (hereinafter, “black floating”). This problem will be explained below using FIG. 1 and FIG. 2.
FIG. 1 illustrates the state of “black floating” in still images. FIG. 1A shows input image 900 (or it may be considered as a modulation state of the optical modulating section). In input image 900, there is a circular object with a high peak brightness on a black background. Note that the broken lines on input image 900 indicate the positions of divided areas of the backlight for ease of understanding, and are not included in the input image. According to this input image, the optical modulating section such as a liquid crystal panel is controlled. To be more specific, the aperture ratio of the liquid crystal panel is controlled such that more light transmits in parts of higher brightness.
FIG. 1B shows the light emitting state of backlight 910. Here, backlight 910 has nine divided areas. Here, assume that the above-described circular object is completely included in the area located in the center of backlight 910 (hereinafter simply “center area”). The center area includes a circular object with high peak brightness in input image 900 as described above, and therefore emits light at brightness matching the image of this area. Then, surrounding areas are turned off because the overall images of these areas are black.
FIG. 1C shows display image 920 displayed on the display apparatus. In this way, in the center area, even black part practically allows a small amount of light to transmit. Therefore, the difference in the brightness of the black color of the background is produced between the center area and the areas adjacent to this center area. As a result, “black floating” is produced distinctly in the center area compared to the neighboring areas.
Although a case of still images has been explained with FIG. 1, a case of moving images will be explained using FIG. 2.
FIG. 2 illustrates the state of “black floating” in moving images. FIG. 2A shows that a circular object moves from the left to the right in same input image 900 as in FIG. 1A.
FIG. 2B shows how the light emitting state of backlight 910 transitions. When the circular object moves to the right and crosses over two light emitting areas, both light emitting areas emit light. Therefore, compared to the time the circular object is included in only one light emitting area, the light emitting area becomes larger. Then, when the circular object moves further to the right, the circular object is included in one area again and only one light emitting area emits light.
FIG. 2C shows how display image 920 displayed on the display apparatus transitions. In this way, when an object having different brightness from the surroundings moves, the area of the above-described “black floating” part changes at the timing the object crosses over light emitting areas. When the area of light emitting areas changes in this way, “black floating” is more likely to be seen.
As a method of reducing such “black floating,” Patent Literature 1, for example, discloses a configuration “having a neighboring area lighting means for making a backlight light the areas of a predetermined width adjacent to non-lighting areas, which are adjacent to divided areas illuminated based on an image signal, at lower brightness than the brightness of divided areas that are illuminated” to perform backlight brightness control.